Second monitor not detected

[Olivares]

I moved home four months ago. In my previous home I occasionally used the TV as a second monitor for my PC. As the distance between PC and TV is now more than in my old home, I today bought a longer (10 m) HDMI cable to connect the two. However, I now find that Ubuntu is not detecting the second monitor. In fact, there is not even a 'detect displays' option showing under settings. My PC is an AMD A10-7700 K APU with Radeon R7 graphics, and I have a partition for Windows on it. (Windows isn't detecting the second monitor either). I tried unplugging the cable / rebooting, also ran command sudo apt update && sudo apt upgrade, but no joy so far. Any suggestions much appreciated. Compressed system info file atatched.system-info.tar.gz.

[nicolasdentremont]

Does the shorter HDMI cable still work? I have a 10 meter HDMI cable that only works on some computers and not on others. My last laptop would only work with it if it was plugged into the charger.

[Olivares]

I can't now find the shorter cable, which is a mystery. Does anybody have any further suggestions?

[Olivares]

I notice that TV input display shows PC as a connected device, while PC does not show TV as being connected. This suggests that there is no fault with the HDMI cable, the problem is in the PC.

[Olivares]

A solution to my problem of getting a second monitor to work via an HDMI cable does not appear to be forthcoming. However, I have now found out that a PC desktop environment can be cast to the smart TV via Chromecast. This is an acceptable solution so this enquiry can now be considered resolved.